1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
Priority is claimed on Japanese Patent Application No. 2008-215328, filed Aug. 25, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
With further miniaturization of semiconductor devices, miniaturized resist patterns smaller than a wavelength limit of an exposure wavelength have been formed by lithography using a conventional exposure. As a method of forming such a pattern smaller than the wavelength limit, a method using oblique illumination such as annular illumination or dipole illumination, which is called a super resolution technology, and a method using a phase shift mask are well known.
Additionally, double patterning has been considered as a method of further miniaturizing a resist pattern. Particularly, a dense contact hole formation has more difficulty in enhancing the resolution than a line-and-space pattern formation, thereby requiring a double patterning method.
The first embodiment of Japanese Patent, Laid-Open Publication No. H05-343279 discloses a double patterning method in which a second resist film is formed over a first resist film after the first resist film is patterned, and then a second exposure is carried out to form an opening that is defined by the first and second resist films and is smaller than the wavelength limit.
On the other hand, Nakamura et al. “Ultra-low k1 oxide contact hole formation and filling using resist contact hole pattern by double L&S formation method” SPIE 6520 (2007) 1E-1 discloses a method of forming a contact hole pattern using double patterning. Specifically, in this method, a first resist pattern is formed and then cured, the second resist pattern is formed over the first resist pattern, and then a hole is formed with the first and second resist patterns as masks.
However, in both the related arts, a second resist film is deposited directly on the first resist pattern, and then the second resist pattern is formed by exposure and developing. For this reason, steps defined by the first resist pattern cause a degradation in the shape of the second resist pattern. Additionally, unless a focus depth of the exposure apparatus such as a stepper is much larger than the depths of the steps of the first resist pattern, it causes a degradation in the resolution upon an exposure of the second resist film.